developer/contributor for Supertux and SuperTuxKart. 3d modeller with a few years experience.
Will_B: we use external programs. Out scripts are for blender, but you could use max or maya, or anything, you would just then have to either import it into blender, or do a lot in work by hand.
and editor has been discussed a bit in IRC (#stk on freenode) and that might come in the future, but for now we use external applications.
P.S. It is the same for karts ;)